Introduction: Pneumothorax in neonates can be life-threatening. In neonates without respiratory distress, spontaneous pneumothorax can also develop under certain conditions.Objectives: To determine the incidence of ultrasonographic signs of pneumothorax in asymptomatic neonates using lung ultrasound as the diagnostic tool.Methods: This was an observational prospective study conducted at the Basurto University Hospital (Bilbao, Spain) between January 2018 and December 2020. Lung ultrasound was performed during routine examination of asymptomatic neonates admitted to the maternity ward.Results: Of a total of 204 asymptomatic neonates included in the study, 21 (10.3%) presented ultrasound signs of pneumothorax (Group A), and 183 (89.7%) had a normal lung ultrasound (Group B). Lung ultrasound was performed after a mean of 19 h of life (range 9-34). The presence of A-lines behind the sternum in the anterior transverse plane, at the intermammillary level, was observed in 100% of patients in Group A compared to no cases in Group B (p < 0.0001). The neonates of Group A presented the lung point located in the midclavicular line, indicative of a mild air leak.Conclusions: Lung ultrasound allows precise detection of suspected small-sized air leaks that can be detected in asymptomatic neonates. The true incidence of pneumothorax in asymptomatic neonates may be substantially higher than previously described in the literature.